The invention starts from a multiphase extraction apparatus having two chambers which are connected in their top and bottom part by connection channels. The chambers are filled with a continuous phase and have separation spaces. They are equipped with dispersion apparatuses and with ports for feeding and removing the feed phase and strip phase.
An apparatus of this type can be used in chemical, hydrometallurgical, microbiological and other industrial branches for separation, extraction, concentration and purification of substances.
Apparatuses for carrying out three-phase liquid extraction processes are known in the form of a two-chamber system, the two chambers being connected together by overflows for the circulation of the continuous phase. The overflows are constructed in the form of tubes which connect together the upper and lower parts of each of the chambers. The chambers are filled with a continuous phase through which two disperse phases, which are not soluble in the continuous phase, are passed in the form of droplets. In this case, substances are transferred from a disperse phase (feed phase) by the continuous phase forming the extraction medium into the other disperse phase (strip phase) (see, for example, Russian Patent Application No. 94-015776/26 of 27.04.94).
These known apparatuses require improvement with respect to their application potential and their performance.
They represent the latest state of the art with respect to design and technical action and are described in more detail below. A conventional multiphase extraction apparatus consists of two chambers filled with a continuous phase. The chambers have apparatuses for dispersing (distributing) the feed phase and strip phase and are connected together by overflows or connection channels for the circulation of the continuous phase. The overflows connect in this case the upper part of the first chamber to the upper part of the second chamber and the lower part of the second chamber to the lower part of the first chamber. The apparatus is equipped with ports for feeding and removing the two disperse phases and has separation spaces which are placed in the area of the inlet orifices of the connection channels (overflows). The phases to be dispersed, feed phase and strip phase, are each divided in the corresponding chamber by an apparatus for dispersion into droplets which then move through the continuous phase as a swarm of droplets. Owing to the difference in density between the dispersion in the first chamber and the dispersion in the second chamber, there is a circulation of the continuous phase through the upper and lower overflows, so that the substance to be separated off is transferred from the feed phase in the one chamber into the strip phase in the other chamber. In this case, the continuous phase in the first chamber serves as extraction medium (and in the second chamber as raffinate phase). A disadvantage of this known multiphase extraction apparatus is that the circulation rate of the continuous phase is only influenced by the density difference between the dispersions in the two chambers; a reduction in this density difference decreases the circulation rate and can lead to a reduced efficacy of the apparatus.
The object underlying the invention is to ensure the efficacy of the multiphase extraction apparatus even in those cases where the density difference between the liquid mixtures in the two chambers is too small to circulate the continuous phase.
This object is achieved according to the invention, starting from the above-described apparatus, by means of the fact that the upper part of the first chamber is connected to the lower part of the second chamber and the upper part of the second chamber is connected to the lower part of the first chamber.
A further development of the invention is characterized in that the two chambers form a separation stage and a number of such separation stages is series connected.
The connection of the upper part of the first chamber to the lower part of the second chamber and of the upper part of the second chamber to the lower part of the first chamber ensures the circulation of the continuous phase even if there is no density difference (based on the mean density of the dispersion in each chamber) between the two-phase liquid mixtures in the one chamber and the other. The circulation arises solely due to density gradients within the individual chambers and by impulse transfer from the droplet swarms, which are produced in the dispersion apparatuses, to the molecules of the continuous phase.
A further advantage is that the two chambers can be operated in cocurrent flow (same direction of motion of continuous phase and disperse phase). The utilization of the two chambers as a separation stage and the series-connection of a number of such stages permits various multistage mass separation processes to be carried out optimally.
FIGS. 1-3 show diagrammatically three possible embodiments of the multiphase extraction apparatus according to the invention.